1. Field of the Invention
This invention relates to a printer suitable for use with a compact desk-top calculator, and particularly to a very useful printer which permits great reduction in the number of components and accordingly can promise a lower cost, greater ease of assembly, much less probability of failure and stable repetitive operation and which eliminates the necessity of adjustment during the manufacture and later fine adjustment.
More particularly, the invention relates to a printer in which a permanent magnet is attached to a rockable printing hammer and a stationary electromagnet device is provided within the range of movement of the permanent magnet or the distribution of the magnetic field of the permanent magnet is expanded to the location where the stationary electromagnet device lies, so that the permanent magnet may be movable within said distribution of the magnetic field. Due to this construction during non-printing, the movable permanent magnet and a normally magnetic material in the electromagnet device attract each other to displace a resilient member coupled to the hammer head and thereby cause the resilient member to accumulate mechanical energy therein; and during printing, a current sufficient to negate at least the magnetic field of the permanent magnet may be supplied to the electromagnet to move the hammer to impact against a character wheel, whereafter the hammer may be quickly and automatically returned to its original position without the use of any special return mechanism.
2. Description of the Prior Art
Most of the heretofore known printers have been intended for use as the high-speed output devices of large electronic computers and have unavoidably been of complicated construction and large size. For example, there is known a printer of the type in which a shank is supported by a pair of plate springs studded perpendicularly to the axis of a character wheel and such shank is attracted by a first electromagnet and released upon operation of a second electromagnet device provided on the first electromagnet, thereby effecting printing. In such printer, however, a special cam mechanism must be provided to return the shank to its original position and this leads to the disadvantage of a complicated and expensive construction. The present invention eliminates such a special return mechanism and is constructed such that a permanent magnet is provided in the printing hammer portion against the conventional point of view to thereby enable the shank to automatically return to its original position and that the magnetic field of the permanent magnet covers the fixed electromagnet device. Also known is a printer in which a magnetic field generating device is provided in the hammer portion to enable use of Fleming's left-hand rule, but again in this type of printer, utilization is made of the coaction of the magnetic field resisting the spring force for returning the shank and therefore, the voltage and the quantity of current used must be considerably great so that the magnetic field generating device must be large in size. In addition, since the construction of this printer is based on the horizontal movement of the shank supported by the pair of plate springs studded perpendicularly to the axis of the character wheel, a space available for the hammer construction is required and this is not suitable for compact printer. Further, during the return of the shank, the repelling force of the shank and the return force of the pair of plate springs are added together to form a great magnitude of energy, which in turn makes it necessary to provide a buffer mechanism and a stop member. Also, adjustment of the stroke length is indispensable and this leads to difficulties in assembly.
The present invention enables realization of a construction in which the electromagnet device itself performs the function of the stop member and also of the buffer mechanism and in which the permanent magnet is accommodated within the hammer head to minimize the size of the printer and reduce the number of parts.